In an effort to understand the molecular mechanism of chemical carcinogenesis, we are studying the interference of 3'-methyl-4-dimethylaminoazobenzene with the expression of the cellular genetic information. One section of our experiments is directed towards characterization of the cytoplasmic binder of the carcinogenic aminoazo dyes, understanding of its function in normal cells and elucidation of its role in the transfer of the carcinogen into the cell nucleus. In the second part of our experiments, we are studying the binding of 3'-methyl-4-dimethylamino-azobenzene to nuclear proteins and changes in the composition and metabolism of chromosomal proteins after the application of the carcinogen. The observed changes are correlated with the changes in the processing of messenger RNA and in its transport to the polysomes.